As illustrated in FIG. 7, a steering apparatus for an automobile is constructed to transmit a rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, and the rotation of the input shaft 3 pushes or pulls a pair of left and right tie rods 4 to apply a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear end portion of a steering shaft 5, and the steering shaft 5 passes in the axial direction through a cylindrical steering column 6, and is rotatably supported by the steering column 6. The front end portion of the steering shaft 5 is connected to the rear end portion of an intermediate shaft 8 by way of a universal joint 7, and the front end portion of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9.
In this kind of steering apparatus, a tilt mechanism for adjusting the up-down position and/or a telescopic mechanism for adjusting the forward-backward position of the steering wheel 1 has been conventionally and widely equipped. In order to construct a tilt mechanism in the steering apparatus, the steering column 6 is supported by the vehicle body 10 so as to be able to pivotally displace around a pivot shaft 11 that is arranged in the width direction (the width direction is the width direction of the vehicle body, and is the left-right direction). Moreover, a displacement bracket that is fastened to a portion near the rear end of the steering column 6 is supported by a support bracket 12 that is supported by the vehicle body 10 so as to be able to displace in the up-down direction and forward-backward direction (the forward-backward direction is the forward-backward direction of the vehicle body). In the meantime, in order to construct a telescopic mechanism in the steering apparatus, the steering column 6 is constructed by telescopically combining an outer column 13 and an inner column 14 so as to be able to freely extend or contract. Further, the steering shaft 5 is constructed by combining an outer shaft 15 and inner shaft 16 by a spline fit or the like so as to be able to freely transmit torque as well as freely extend and contract. In the illustrated example, an electric power steering apparatus which reduces the force required for operating the steering wheel 1 by using an electric motor 17 as an auxiliary power source is also assembled.
In the case of a manual tilt mechanism and telescopic mechanism, a state of being able to adjust a position of the steering wheel 1 and a state of securing the steering wheel 1 after adjustment are switched by operating an adjustment lever. Various kinds of construction are conventionally known for such a manual tilt mechanism and telescopic mechanism. For example, in the case of the construction illustrated in FIG. 7, long holes 19 in the forward-backward direction that extend in the axial direction of the outer column 13 are formed in the displacement bracket 18 that is fastened to the outer column 13. Moreover, the support bracket 12 has a pair of support plate portions 20 that hold the displacement bracket 18 from left and right sides, and long holes 21 in the up-down direction in portions of the support plate portions 20 that are aligned with each other. An adjustment rod 22 is inserted through the long holes 21 in the up-down direction and the long holes 19 in the forward-backward direction. A pair of pressure portions are provided on this adjustment rod 22 on both side in the width direction of the pair of support plate portions 20 to hold the pair of support plate portions 20, and an expansion and contraction apparatus that operates based on the operation of the adjustment lever 23 (see FIG. 8) enable a space between these pressure portions to expand or contract.
When adjusting the up-down position and the forward-backward position of the steering wheel 1, the expansion and contraction apparatus expands the space between the pressure portions by turning the adjustment lever 23 in a specified direction (typically, downward). In this state, the surface pressure at the sliding contact portion between the inside surfaces of the support plate portions 20 and the outside surfaces of the displacement bracket 18 is reduced or lost. In this state, the position of the steering wheel 1 can be adjusted by displacing the outer column 13 within the range that the adjustment rod 22 is capable of displacing inside the long holes 21 in the up-down direction and the long holes 19 in the forward-backward direction. After the steering wheel 1 has been moved to a desired position, the adjustment lever 23 is rotated in an opposite direction of the specified direction to contract the space between the pressure portions, such that the displacement bracket 18 is firmly held by the support plate portions 20 from both sides in the width direction thereof. As a result, the steering wheel 1 is maintained in an adjusted position.
This kind of steering apparatus is also often equipped with a mechanism for protecting the driver from impact during a secondary collision that occurs when the driver collides with the steering wheel when an automobile is in a collision accident or the like. The construction of this kind of mechanism is widely known, as disclosed in JP S50-55034 (A), JP H01-249571 (A), JP 2000-043738 (A), JP S59-147673 (U), JP H01-175968 (U), and JP 2,595,547 (Y2). JP 2000-043738 (A) and JP 2,595,547 (Y2) disclose a tilt steering apparatus having construction in which by forming a slit next to tilting long holes that are formed in support plate portions of a support bracket, part of the support bracket plastically deforms, which reduces the impact that is applied to the driver's body during a secondary collision. However, the construction disclosed in JP 2000-043738 (A) is for a tilt steering apparatus for a cab-over-engine automobile in which the angle of the center axis of the steering column with respect to the horizontal direction is about 58 degrees to 75 degrees (angle near vertical). Therefore, construction for allowing part of the support plate portions to plastically deform during a secondary collision is also special and cannot be applied to a tilt steering apparatus for a typical automobile in which the center axis of the steering column is close to the horizontal direction (the angle of the center axis with respect to the horizontal direction being about 10 degrees to 40 degrees).
On the other hand, JP 2,595,547 (Y2) discloses construction that, part of the support plate portions plastically deforms when a steering lock mechanism has collided with the rear end edge of the support plate portions due to a secondary collision. This conventional construction is effective in the case of a steering apparatus having construction in which, when the steering column has displaced forward due to a secondary collision, the steering lock mechanism collides with the rear end edge of the support plate portions before impact energy is applied to the adjustment rod. However, in the case of typical construction in which the adjustment rod is strongly pressed against the front edges of the long holes in the up-down direction, it is not always possible to reduce the impact that is applied to the driver's body.
Furthermore, JP 2010-052639 (A) discloses construction for preventing a steering wheel to displace upward as a secondary collision proceeds. In this construction, as illustrated in FIG. 8, regardless of the up-down position of the steering wheel 1 (see FIG. 7), the inclination angle α of long holes 21a in the up-down direction with respect to a virtual plane A that is orthogonal to the center axis of the steering column 6a is greater than the inclination angle β (installation angle of the steering column 6a) of the center axis of the steering column 6a with respect to the forward-backward direction B (α>β). By making the inclination angle α of the long holes in the up-down direction greater than the installation angle β of the steering column 6a, displacement of the adjustment rod 22 such that the adjustment rod 22 rises upward along the hole 21a in the up-down direction is prevented regardless of the component force that occurs due to engagement between the outer circumferential surface of the adjustment rod 22 and the front side edges of the long holes 21a in the up-down direction due to a secondary collision. In this case, it is possible to properly maintain the collision position between an airbag installed in the steering wheel 1 and the driver, and thus it is possible to ensure the effect of the airbag reducing the impact. Moreover, it is possible to effectively transmit the force that acts during a secondary collision in a direction that causes the entire length of the steering column 6a to contract such that the impact is smoothly absorbed by the contraction of the steering column 6a. However, even in JP 2010-052639 (A), technology for reducing the impact that is applied to the driver's body when the adjustment rod 22 is forcibly pressed against the front edges of the long holes 21a in the up-down direction is not disclosed.